The image above shows the harvesting of salt from the Cargill salt ponds on the southern end of Bonaire, WI.
There are just two employees - one operating the Caterpillar dozer and one driving the Caterpillar belly dump. The belly dump is filled to overflowing in just a few minutes. Much of this salt gets shipped by sea to the icy parts of North America for road de-icing.
The image below is a copy of a black and white photo (the original of which is in a museum on Bonaire - not sure of the date) showing two laborers using picks to break the salt crust on the same salt ponds, while a third laborer lifts the broken chunks of salt onto a wheel barrow.
All human energy - no Diesel fuel!
Links:
[1] http://66.228.45.157/system/files/salt-pan-evaporation-harvesting-cargill-caterpillar-bonaire-1-DSC00187-4.jpg
[2] http://66.228.45.157/system/files/Salt-ponds-Bonaire-workers-slaves_maybe_black-and-white-historic-photo-using-wheelbarrows-to-haul-salt-DSC00106.jpg